The subject of the investigation is the strain that occurs when reinforcement occurs as a result of a fixed number of performances compared with the more durable maintenance that usually characterizes other schedules of reinforcement. A series of experiments investigates the function of the "number of pecks" as a controlling reinforcing and discriminative stimulus by the use of visual, added counter which parellels the function of the bird's own behavior. The proposal tests the hypothesis that the predominant control by "number of pecks" in fixed-ratio schedules is to weaken the performance compared with other schedules where the relation is ambiguous.